1. Field of the Invention
The present invention relates generally to heat exchangers, and particularly to a double heat exchanger having plural heat-exchange cores such as a condenser core of a refrigeration cycle and a radiator core for cooling engine coolant.
2. Related Art
JP-A-10-103893 discloses a double heat exchanger having a radiator and a condenser. A header tank of the radiator has plural protrusions each of which protrudes from an outer wall of a header tank of the radiator and contact an outer wall of a header tank of the condenser so that a gap is securely formed between the header tank of the condenser and the header tank of the radiator. As a result, heat transfer from the header tank of the radiator having a high temperature to the header tank of the condenser having a low temperature is restricted.
However, in the above-mentioned double heat exchanger, when the protrusions are brazed to the header tank of the condenser, melted brazing material flows to be collected at a contact portion between each of the protrusions and the header tank of the condenser by capillary action. Therefore, when a brazing process of the protrusions is completed, a size of each of the protrusions may be increased by the brazing material collected at the contact portion. As a result, an area of the contact portion through which heat is transferred from the header tank of the radiator to the header tank of the condenser is increased. Therefore, an amount of heat transferred from a core portion of the radiator to a core portion of the condenser may be increased, and a heat radiation performance of the core portion of the condenser may be declined.
Further, in the above-mentioned double heat exchanger, the protrusions are formed on the header tank of the radiator to be away from each other with an interval in a longitudinal direction of the header tank of the radiator. Therefore, when the header tank of the radiator is formed by extrusion or drawing to have an uniform cross-section along a whole length of the header tank of the radiator in the longitudinal direction thereof, it may be difficult to integrally form the protrusions with the header tank of the radiator.